There is described a tool for clamping a saver sub assembly of the drive shaft of a top drive drilling machine, characterized more particularly by a tong, which is arranged to hold the saver sub assembly fixed by releasable abutment against a portion of the saver sub assembly, being arranged on an upper portion of a frame which, in a position of use, is attached in a rotationally rigid manner to and projects from a support, the frame being provided with a through-going centre opening arranged to receive a substantial portion of the saver sub assembly. A method of replacing a saver sub assembly on the drive shaft of a top drive drilling machine is described as well.
When a top drive drilling machine is used, for example in exploration and production drilling for oil and gas, one or more subs with varying functions is/are arranged between the drive shaft and the drill string. A sub may work solely as a replaceable wear part for the threads of the drive shaft not to be ruined by constantly being connected and disconnected. Such a sub may remain connected to the drive shaft until it must be replaced because of wear. Another type of sub may include safety valves for controlling the fluid pressure in the drill string, typically one or more so-called IBOPs (Internal Blowout Preventers). Such a sub must be demounted regularly for necessary valve inspection. Because of adjacent elements, for example frame details, ordinary pipe tongs that are used to connect and disconnect pipe sections have a range that makes it impossible to use them to demount and mount said subs, as the drilling machine will abut on the tong before the tong jaw encircles the sub. To demount or mount subs of this kind it is therefore usual to position provisionally a separate rig tong around the sub by means of a lifting tackle and a stack of pallets, for example. This work entails a great risk of personnel injury, and the operation is time-consuming and therefore expensive, as the drilling will have to be stopped for this period.